Technology using an LED (Light-Emitting Diode) is now receiving attention as the light source of a projector that projects an image on a screen such as a liquid crystal projector or a DMD (Digital Micromirror Device) projector (see Patent Document 1).
Because an LED features long service life and high reliability, a projector that uses an LED as a light source has these advantages of long service life and high reliability. In addition, an LED can be caused to flash on and off at high speed and can thus broaden the range of color reproducibility of an image.
However, as the light source for a projector, the light of an LED typically has low luminance, and obtaining an image with sufficient luminance is therefore problematic in a projector that uses an LED as a light source. The degree to which light from a light source can be used as projection light on a display panel is limited by étendue. Specifically, light from a light source cannot by efficiently employed as a projection light if the value of the product of the emitted light area of the light source and the radiation angle is not suppressed to a value equal to or less than the value of the product of the area of the incident surface of the display panel and the acceptance angle that is determined by the f-number of the illumination optical system.
In a light source realized by an LED, increasing the emitted light area can raise the quantity of light, but increasing the emitted light area also increases the étendue of the light source. Although increasing the quantity of light without increasing the light emission area is desirable as a light source of a projector due to the limits of étendue, increasing the quantity of light without increasing the emission light area is problematic in a light source realized by an LED.
In contrast, methods of obtaining fluorescence with high luminance include a method of irradiating a laser light upon a phosphor to obtain fluorescence by excitation. In this method, fluorescence that has greater luminance than an LED can be obtained efficiently by the appropriate selection of the fluorescent substance.